1. Field of the Invention
The present invention relates to a preform heating device used in a blow molding device in which a preform formed by injection molding or extrusion molding is heated and subsequently blow molded, and in particular to a preform heating device having a plurality of infrared heaters spaced apart in the axial direction of the preform.
2. Prior Art
A preform heating device having a plurality of infrared heaters spaced apart in the axial direction of the preform is described for example in U.S. Pat. No. Re. 34,177 and U.S. Pat. No. 5,549,468.
In U.S. Pat. No. Re. 34,177, an adjustment means is provided whereby during the forming process, an operator can adjust the heater positioning from the exterior of the device to move the heaters closer to or further away from the preforms.
In U.S. Pat. No. 5,549,468, as in U.S. Pat. No. Re. 34,177, the problem is discussed that if the operator is able to adjust the heater positioning in an arbitrary way, accurate repetition under the same conditions is not possible, and it is proposed that the heating box be removed, and the heaters adjusted to accurate positioning using a separately provided adjustment jig.
Furthermore, in U.S. Pat. No. 5,549,468, it is proposed that in addition to the horizontal heater positioning adjustment, the heater positioning be adjustable in the vertical direction.
In Japanese Patent Application Laid-Open No. 8-132517, a previous proposal by the applicant of the present application, a blow molding device for small-scale manufacture is disclosed. In this blow molding device, a heating box is adjustable on a base in the vertical direction and also towards and away from the preforms, and further, within the heating box a pair of heaters is adjustable in the vertical direction and also towards and away from the preforms with respect to a rod extending vertically within the heating box.
However, the adjustment of the heater positioning within the heating box of a blow molding device is carried out infrequently, and generally in a fabrication plant a single blow molding device is often used for several years to make the same bottle or other product, and even when there are limited design changes in a bottle the adjustment can be achieved by adjustment of the heater voltage.
For this reason, the task of adjusting the heater positioning is only required when the device is originally set up for blow molding, and when there is a change to a completely new preform, bottle, or other molded product from previously.
Therefore, a construction as disclosed in U.S. Pat. No. Re. 34,177, in which the operator frequently adjusts the positioning of the heaters during the forming process is undesirable.
Further, as described in U.S. Pat. No. 5,549,468, the onerous task of removing the heating box in order to adjust the heater positioning, and the requirement to provide a special jig for the sole purpose of adjustment is a burden on the operator.
Furthermore, for a blow molding device for small-scale manufacture as disclosed in Japanese Patent Application Laid-Open No. 8-132517, compared with conventional devices for large-scale manufacture, replacement of a mold for different molded products has become more common.
Thus, when adjusting the molding conditions, the heater adjustment is more frequently required for positioning adjustment in the vertical direction than in the positioning closer to or further away from the preforms, and therefore an improvement in the ease of carrying out heater positioning adjustment is desirable.